na-adjective, noun
amorphous; shapeless
Describes something lacking a fixed or definite shape; used in both literal and figurative contexts.
この物質は無定形で、結晶構造を持たない。
This substance is amorphous and has no crystalline structure.
彼の考えはまだ無定形だ。
His ideas are still shapeless.
Compound of 無 (mu, 'without') and 定形 (teikei, 'fixed form'). The exact historical derivation is uncertain, but the word follows a standard Sino-Japanese pattern.