Alternation.
yttrium
romantic
Quorum is a government term. It begins with the letter q.
quadrilateral quadrilateral
Linear or Line
Hierarchical is a classification term. It means arranged in the order of rank.
A good scientific term beginning with x is x-ray.
Joule is a science term. It is a unit of energy.
Zirconium is a chemical element. It begins with the letter Z.
Alliteration
Young ice is newly formed thin ice flat on a sea or lake. It begins with the letter Y.
Yellow Tavern (Virginia) was the scene of a battle during the Civil War. It begins with the letter Y.