En-
Per-
Semi-
Mystery
100

Enclose

Cause to be closed

100

Perspective

Inclined to see through

100

Seminnual

Happening every half a year 

100

Entrust

cause to trust

200

Enable

Cause to be able

200

Permanent

Lasts through the years; lasts forever

200

Semicircle

Half of a circle

200

Permit

To allow through

300

Enlighten

Cause to be in light

Realistic: to give knowledge

300

Permeate

Cause to go through

300

Semicolon

A type of punctuation using half of a colon

;

300

Perennial

Bonus: 

enn - yearly

Through the years

400

Enjoyable

Cause to be able to have joy
400

Persevere

To not give up, no matter what you go through

400

Semifinal

Happening partway to the finals

400

Semiweekly

Happening every half of a week (two times weekly)