Third person singular present tense of 'grouse'; complains or grumbles, or plural noun meaning multiple grouse birds.
From 'grouse' as both a verb (to complain) and noun (the bird). The verb forms follow regular conjugation; plural noun adds '-es' due to the sibilant ending.
The word 'grouses' is beautifully ambiguous—someone might say 'He grouses about the weather' (verb) while 'The hunters bagged three grouses' (noun plural), using the same word in two completely different ways.
Complete word intelligence in one call. Free tier — 50 lookups/day.