1.uniform的意思是“制服”,是可数名词。
2.in uniform可表示“(穿着)制服,服役”,也可表示“军人”,是不可数名词。

The new uniforms will arrive tomorrow.新制服明天就到。
The headmaster elaborated upon the idea for a new school uniform.校长就新校服的想法作了说明。
Soldiers, policemen, and nurses wear uniforms.士兵、警察和护士们都穿制服。
The coach checked in the football uniforms at end of the school year.在学年结束时,教练把足球球衣收回并登记。
He was in uniform three years.他服役三年。
When evening came, the streets still remained full of military uniforms.夜晚来临时,大街上仍然到处是军人。

uniform用作形容词时意思是“全都相同的,一律的,清一色的”,在句中可用作定语或表语,用作表语时,常接in引起的短语。

用作定语
▲～+n.
All these sticks are of uniform length.所有这些手杖长度都是一样的。
The earth turns around at a uniform rate.地球以相同的速度旋转。
用作表语
▲S+be+～
The windows in the house are all uniform.房子里的窗户都是一样的。
▲S+be+～+prep.-phrase
They are uniform in size and shape.它们的大小和形状都相同。
The trees were uniform in height.那些树长得一般高。

［派生词］ uniformly adv. 全都相同地,一律地,清一色地‖uniformity n.无差异; 无变化
［同义词］ n.  costume, dress, suit adj.  alike, consistent, equal, like, same, similar
［反义词］ adj.  changing, varied