The word 'unplain' refers to something that is not simple or straightforward. There are several synonyms that can be used in place of this word to convey a similar meaning. One such synonym is 'complicated', which suggests that something is composed of several interrelated parts, making it difficult to understand or deal with. Another synonym for 'unplain' is 'complex', which implies that something is made up of intricate or interrelated parts that are difficult to unravel. Other synonyms for 'unplain' include 'intricate', 'fancy', 'sophisticated', 'convoluted', and 'challenging'. All these words convey the same sense that something is not straightforward and requires a deeper understanding to comprehend.