This is the 3772nd most frequent Polish word.
mucha
The Polish word "mucha" means "fly" (the insect) in English.
Here, 'mucha' refers to a bow tie, which is a common secondary meaning of the word in Polish.
Mucha od garnituru dobrze wygląda.
The bow tie matches the suit well.
In this idiomatic expression, 'muchy' (plural of 'mucha') is part of the phrase 'mieć muchy w nosie', meaning to be in a bad mood or annoyed, showing an idiomatic usage.
Ależ ona ma muchy w nosie!
My, she is in a bad mood!
In this sentence, 'mucha' is used as a noun referring to the insect ‘fly’.