まほし

Shift from まくほし (-makuhoshi), itself a compound of ま (-ma, the 未然形(みぜんけい) (mizenkei, “irrealis form”) of む (-mu, volitional/conjectural auxiliary verb)) +‎ く (-ku, nominalizing suffix) +‎ ほし (hoshi, classical form of ほしい (hoshii, “wanted, desirable”)).

One alternative derivation posits that this may have derived from the volitional/conjectural auxiliary む (-mu) in the irrealis form of ま (-ma), with ほし (hoshi) attaching directly to this. However, syntactically, hoshi never followed verbs in the irrealis, and only followed nouns or verbs in the conjunctive -te conjugation, making this derivation unlikely.

The older form まくほし (-makuhoshi) appears in Old Japanese works of the Nara period and early Heian period, with this abbreviated まほし (-mahoshi) form arising later in the Heian period, primarily in waka poetry and works written in kana. The modern desiderative ending たい (-tai) then appears from the Kamakura period, gradually replacing -mahoshi.

• IPA^(key):

まほし • (-mahoshi) 

1. (archaic) following the irrealis stem of verbs
   1. to want (to do); to hope (to do)

      Synonym: たい

      • 1059, 菅原孝標女, 『更級日記』

        つゞきのみまほしくおぼゆれど

        tsuzuki no mimahoshiku oboyuredo

        Although I want to read the story after it...

   2. (only used after ある) I wish that; it is desirable that
      • 1349, 吉田兼好, 『徒然草』 52

        先(せん)達(だつ)はあらまほしきことなり

        sendatsu wa aramahoshiki koto nari

        It is better to have someone guiding you.