From Old English *fostrian*, "to nourish, feed, support," derived from *fōstor*, meaning "food, nourishment," which itself traces back to Proto-Germanic *fōstrą*. The sense of raising or caring for a child who is not one's own is recorded from the 13th century, while the broader figurative sense — nurturing ideas, feelings, or qualities — emerged strongly in Early Modern English.

In everyday American and British English, *foster* is widely used in the phrase "foster care," referring to the system in which children are temporarily placed with licensed caregivers. Beyond this, the word thrives in professional and academic contexts: you'll routinely see phrases like "foster innovation," "foster teamwork," or "foster a sense of community" in business writing, policy documents, and education — making it a high-value word for learners who want to sound fluent in formal registers.