a. [ L. indeclinabilis: cf. F. indéclinable. See In- not, and Decline. ] (Gram.) Not declinable; not varied by inflective terminations; as, nihil (nothing), in Latin, is an indeclinable noun. -- n. An indeclinable word. [ 1913 Webster ]
(adj) not capable of being precisely or readily described; not easily put into words, Syn. undefinable, Example:an indefinable feeling of terror; an abstract concept that seems indefinable