No, the terms parallel and congruent are not synonymous.
Yes, lines can be congruent yet not parallel.
Explanation:
Congruent lines are the lines that are equal in length i.e congruency is determined by the size of the lines under consideration. Congruency refers to equality between two items.
Whereas parallel lines are lines in a plane which never meet each other no matter how much there length is increased, they never cross or interesect each other.
Congruent lines may or may not interesect each other but parallel lines never intersect.