Ha

• POS: Interjection, Noun

CIDE DICTIONARY

Ha, interj. [AS.].

 An exclamation denoting surprise, joy, or grief. Both as uttered and as written, it expresses a great variety of emotions, determined by the tone or the context. When repeated, ha, ha, it is an expression of laughter, satisfaction, or triumph, sometimes of derisive laughter; or sometimes it is equivalent to “Well, it is so.”  [1913 Webster]
"Ha-has, and inarticulate hootings of satirical rebuke."  [1913 Webster]

OXFORD DICTIONARY

Ha, symb. Chem. the element hahnium.

Ha, int. & v. (also hah)
--int. expressing surprise, suspicion, triumph, etc. (cf. HA HA).
--v.intr. (in hum and ha: see HUM(1))

Ha, abbr. hectare(s).