In the tachanun of Monday and Thursday, we say "ותראה לפניך עקידת יחיד למען ישראל". The binding is referred to as the akeidat yachid (which refers to Yitzchak via Bereishit 22:2 "מה שנעקב יצחק שכתי' קח נא את בנך את יחידך" (taken from פירושי סידור התפילה לרוקח [סט] אנא מלך חנון ורחום) . A quick look in the Bar Ilan responsa and google shows that the phrase never appears in the tanach text, talmud or medrash.
Is there any discussed significance to this construction as distinct from naming Yitzchak (the phrase Akeidat Yitzchak appears once in the Talmud -- Bavli, Rosh Hashana, perek 1 and often in the Medrash). Is it stylistic or does it import meaning that would otherwise be missing from the prayer?