Jonnie Robinson, Curator, English accents and dialects, British Library Sound Archive, writes:
Polari is a language that was once extremely common among the gay population of the United Kingdom as a means of communicating with like-minded people at a time when speakers perhaps felt they had more need of a private slang. It probably had its heyday in the 1960s and was indeed regularly featured on the BBC radio programme 'Round the Horne'. Its vocabulary is a wonderful combination of words from various sources: Romany, Yiddish, Italian, canal-speak, theatre-speak, rhyming slang and back-slang. In many ways it resembles other secret languages, such as children's codes or butcher's back-slang - means of communication that send out a strong signal of membership to the initiated, while excluding those outside the target group. The word polari itself, meaning to chat, derives from the Italian verb parlare, meaning to talk.
The words mentioned here would at one time have been widely understood in gay circles. Vada means to see; eek is an abbreviation of ecaf, back-slang for face; dolly means handsome; riha is hair, so rihary means hairy; lally is a leg; bona means good and is still widely used in gay publications; omi means man and polone means woman. The word naff, originally a polari word meaning bad or drab has entered into British mainstream slang.