Being an essential and permanent part of something.
Being an included feature that normally comes as an extra.
Constructed as a non-detachable part of a larger structure.
Anything (such as a piece of furniture, or a software feature) that is built in, not added as an extra.
Incorporating all of the fittings into connected units.
simple past tense of fit ("to tailor, to change size")
simple past tense of fit (other senses)