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Phrase(s): purr like a cat [and] purr like a kitten
1. Fig. [for an engine] to run well and smoothly. • My car really purred after I got it tuned up. • New spark plugs and this old heap will really purr like a cat. 2. Fig. [for a person] to be very pleased, and perhaps moan or purr with pleasure. • She was so pleased that she purred like a cat. • Sarah really purrs like a kitten when she is happy.
McGrawhill's American Idioms And Phrasal Verbs