(sequence, idiomatic) Firstly; before anything else.

(rugby) The first player to receive the ball, from a scrum-half (or acting scrum-half). This is often the fly-half, but may be a different player if the fly-half is unavailable, or a forward who will drive.

One of ninety-one equal parts of a whole.

The ordinal form of the number fifty-one, describing a person or thing in position number 51 of a sequence.

The basic idea of how to do something. / Used other than figuratively or idiomatically: see first, thing.

The ordinal form of the number ninety-one, describing a person or thing in position number 91 of a sequence.

One of sixty-one equal parts of a whole.

The ordinal form of the number sixty-one, describing a person or thing in position number 61 of a sequence.

One of fifty-one equal parts of a whole.

A basic, foundational proposition or assumption that cannot be deduced from any other proposition or assumption.