Paul M. Conner, O.P., Celibate Love p. 23 (PDF p. 27), claims:
In Hebrew the terms "sister" and "bride" do not always have literal application. Often they are interchangeable. Frequently, too, "sister" can mean "friend." The context decides the meaning.
Is this true? If so, what are some examples where "'sister' and 'bride'…Often…are interchangeable" and where "'sister' can mean 'friend'"?
The quoted opinion by the OP is mistaken and based on a figurative reading of the verses in Shir haShirim (Song of Songs), which is written in a language of metaphore. The text is talking about very deep secrets in a relation between G-d represented by king Sh'lomo (Solomon) and the nation of Israel (his beloved). There are several verses in Shir haShirim, where the word "sister" and "bride" are used together:
לִבַּבְתִּ֖נִי אֲחֹתִ֣י כַלָּ֑ה לִבַּבְתִּ֙ינִי֙ באחד [בְּאַחַ֣ת] מֵעֵינַ֔יִךְ בְּאַחַ֥ד עֲנָ֖ק מִצַּוְּרֹנָֽיִךְ׃ מַה־יָּפ֥וּ דֹדַ֖יִךְ אֲחֹתִ֣י כַלָּ֑ה מַה־טֹּ֤בוּ דֹדַ֙יִךְ֙ מִיַּ֔יִן וְרֵ֥יחַ שְׁמָנַ֖יִךְ מִכָּל־בְּשָׂמִֽים׃ נֹ֛פֶת תִּטֹּ֥פְנָה שִׂפְתוֹתַ֖יִךְ כַּלָּ֑ה דְּבַ֤שׁ וְחָלָב֙ תַּ֣חַת לְשׁוֹנֵ֔ךְ וְרֵ֥יחַ שַׂלְמֹתַ֖יִךְ כְּרֵ֥יחַ לְבָנֽוֹן׃ גַּ֥ן ׀ נָע֖וּל אֲחֹתִ֣י כַלָּ֑ה גַּ֥ל נָע֖וּל מַעְיָ֥ן חָתֽוּם׃ ... בָּ֣אתִי לְגַנִּי֮ אֲחֹתִ֣י כַלָּה֒ אָרִ֤יתִי מוֹרִי֙ עִם־בְּשָׂמִ֔י אָכַ֤לְתִּי יַעְרִי֙ עִם־דִּבְשִׁ֔י שָׁתִ֥יתִי יֵינִ֖י עִם־חֲלָבִ֑י אִכְל֣וּ רֵעִ֔ים שְׁת֥וּ וְשִׁכְר֖וּ דּוֹדִֽים׃
You have captured my heart, My sister, my bride, You have captured my heart With one [glance] of your eyes, With one coil of your necklace. How sweet is your love, My sister, my bride! How much more delightful your love than wine, Your ointments more fragrant Than any spice! Sweetness drops From your lips, O bride; Honey and milk Are under your tongue; And the scent of your robes Is like the scent of Lebanon. A garden locked Is my sister, my bride, A fountain locked, A sealed-up spring. ... I have come to my garden, My sister, my bride; I have plucked my myrrh and spice, Eaten my honey and honeycomb, Drunk my wine and my milk.
It is certainly meaningless to speak about these verses figuratively as one cannot marry a sister. The commentary Divrei Yedidyah by R' Aryeh Leib Lipkin explains the metaphorical meaning of the words My sister and My bride, p.41 of the downloaded file on verse 4:9:
To summarize, G-d refers to the nation of Israel as both My sister and My bride to indicate that the love that exists between them is based on two factors:
There is no connection here for the case of two people building a family as usually the possible links between parents and other ancestors have little impact on the relation that two people create.
כּלּה kallâh (< כּלל kâlal "to make perfect") = bride, spouse
אחות 'âchôth = sister (literally or figuratively)
These words occur interchangeably in:
Song of Solomon 4:9-10,12:
Thou hast wounded my heart, my sister, my spouse, thou hast wounded my heart with one of thy eyes, and with one hair of thy neck. How beautiful are thy breasts, my sister, my spouse! thy breasts are more beautiful than wine, and the sweet smell of thy ointments above all aromatical spices. […] My sister, my spouse, is a garden enclosed, a garden enclosed, a fountain sealed up.
Let my beloved come into his garden, and eat the fruit of his apple trees. I am come into my garden, O my sister, my spouse, I have gathered my myrrh, with my aromatical spices: I have eaten the honeycomb with my honey, I have drunk my wine with my milk: eat, O friends, and drink, and be inebriated, my dearly beloved.
ריע רע (friend, companion, lover, neighbor, brother or sister) appears in Song 5:1.
One would be remiss not to mention the oft-repeated theme in Genesis, of people pretending that their wives were their sisters for fear of the natives. Avraham in Egypt and in the land of the Philistines, and Yitzchak also in the land of the Philistines. The poster's observation makes their deception more indirect.
