late 14c., polet, "young fowl" (late 13c. as a surname), from Anglo-French pullet, Old French poulette, poilette, diminutive of poule, poille "hen," from Vulgar Latin *pulla, fem. of Latin pullus "young animal," especially "young fowl" (source also of Spanish pollo "chicken," Italian pollo "fowl;" from PIE root *pau- (1) "few, little." Compare pony.
A cockerel is a male bird under one year old, a cock over one year old. A hen is a female over one year old and a pullet under one year old. [U.S. Department of Agriculture, "Practical Poultry Production," 1920]