ἄσιγμος

ον
A. without sigma, ᾠδαί D.H. Comp. 14; ἄ. ᾠδή, name of a poem of Lasus without a sigma in it, Ath. 10.455c:—hence ἀσιγμοποιέω, compose such a poem, ibid.
Liddell, Scott & Jones
A Greek-English Lexicon, 1940
An open-access project