Aria "Vesti la giubba" from Ruggero Leoncavallo's opera Pagliacci begins with the word "recitar". It is translated into English as "act". If I am not mistaken "recitare" is closer to the English "recite" rather than "act". Also, there is no "recitar" in standard Italian. It sounds like it should be "recita" if it is second person imperative. Please explain this word.
The verb recitare can mean to act. Meaning 2 in the Treccani dictionary entry says
Interpretare un’opera teatrale, cinematografica, radiofonica o televisiva, o una parte di un’opera
The form recitar is a truncation used, in this case, to fit the metric of the verses.
The character singing the aria, Canio, has just discovered his wife's infidelity, but has to dress as a clown and act notwithstanding his life problems. So he starts off with Recitare! (truncated for metric reasons), that can be loosely translated as “Alas! I have to act!”