mostwhat

mostly; for the most part

Adverb

  1. mostly; for the most part
    • All the rest do mostwhat far amiss. - 1595, Ed. Spencer [i.e., Edmund Spenser], “Colin Clouts Come Home Againe”, in Colin Clouts Come Home Againe, London: […] T[homas] C[reede] for William Ponsonbie, →OCLC:

Origin

From most + what.