x1=v1=z1 is an irregular/free-form content word meaning x2=v2=z2 in language x3=v3 (usually Lojban); x1 is a stage-4 or stage-3 fu'ivla.
A zi'evla is any non-gismu, non-lujvo, non-cmevla (see brivla–cmevla merger) valid brivla. This generalizes the concept of fu'ivla to reflect the fact that many free-form brivla in Lojban nowadays are completely novel words not borrowed from any other languages; instead, many are created by splicing together other Lojban words, similar to lujvo but without adhering to any regular morphological patterns. Synonymous with zevla; mostly synonymous with u'ivla and vonfu'ivla; refers also to gimyzevla; contrast with zevlyjvo/brapagjvo and valtcizbaga (which are lujvo, not zi'evla).