Noun
(historical numismatics) A silver coin with a face value of one and a half pence (1½d.):
Such an English coin (1½d.), minted 1561–1582.
Such a British coin (1½d. = £⅟₁₆₀), minted 1834–1843 and 1860–1862 for circulation in the colonies of the British Empire (chiefly Ceylon and the West Indies).
(dated, UK) A money of account equal to 1½d.
Source: en.wiktionary.orgthree-halfpence