Something that gives pleasure, diversion, or amusement. The acrobatics on the stage were entertainment for the audience. The daily crossword puzzle is an excellent form of entertainment for many people.
From Middle English entretenement, from Old French entretenir “to hold in,” probably from the Latin inter- “among” (see inter-) + tenir “to keep up, support” (from tenere, from the Indo-European root ten- “to stretch”). The sense of “gratify, amuse” is late 15c.
The suffix -ment is common in English, forming nouns from verb stems and other words that end in –er or –ance (amazement, betterment, merriment). It was also borrowed from French, where it replaced the Latin -mentum (now –mentum) when inserted with verb stems ending in -er or -ance. See also amusement, divert, gratify, pleasure, and work.