Radak (Y'sha'ya 28:4) comments that ציץ is the masculine form and ציצית is the feminine form:
נזכר בלשון זכר ציץ ובלשון נקבה ציצית
The Zohar (Sh'lach 174b) likewise notes this. The Zohar understands this connection as representing a kabbalistic dichotomy where ציצית represents the feminine aspects of Creation and the physical world while the ציץ represents the masculine and the spiritual world. The Zohar also notes that while only a kohein could don the tzitz, the commandment of tzitzis applies to all Jewish men:
ציצית איהו נוקבא רזא דעלמא תתאה אסתכלותא לאדכרא ציץ דכר ציצית נוקבא ודא לכל ב"נ, ציץ לכהנא
As a point of comparison, the Zohar remarks that both the tzitz and tzitzis are meant to be displayed and seen.
Note that ציץ also means "flower" (e.g. Y'sha'ya 28:4, 40:6-8).