The Collaborative International Dictionary of English v.0.48:
open-collared \open-collared\ adj. not buttoned at the neck; -- of a shirt; as, dressed casually in shorts and an open-collared shirt. [WordNet 1.5]WordNet (r) 3.0 (2006):
open-collared adj 1: of a shirt; not buttoned at the neck; "dressed casually in shorts and an open-collared shirt"