Question

what is the literal meaning of sine, cosine, tan and theta?

Answer 1

Sin means.....Curve

Cosine means....Complementary angle

Tan means.......A tangent of a triangle

Theta.....is used for any unknown values of a triangle

Answer 2

the ratio of opposite side of an angle(measure of angle) and length of the hypotenuse is constant in all similar right angle triangles.
this ratio will be named as "sine" of the angle.
similarly
adjacent side of an angle θ/ hypotenuse = cosine θ
and
ratio of opposite side and adjacent side of an angle is constant and it can be named as " tangent" of that angle.
cosec, sec and cot are respectively the reciprocals of sin, cos, tan
some times , the Greek letter θ (theta) is used to denote an angle.
with out angle there is no meaning to sin , cos and tan
the first use of the idea of 'sine' in the way we use it today was in the book Aryabhattiyam by Aryabhatta.
Aryabhatta used the word ' ardhajya' for the half chord,which was shortened to 'jya' or 'jiva' indue course.
when Aryabhattiyam was translated into Arabic , the word jiva was translated into 'sinus', which means curve.
it translated to Latin it become 'sinus', also used as sine, become common in mathematical texts throughout Europe.
An english professor of astronomy Edmund Gunter first used the abbreviated notation 'sin'.
cosine. was originally written "co.sine," short for Complement sinus.
Tangent comes from the latin Tangens , the present participle of Tangere,"to touch" it means "touching"