キョウ, おそ.れる, おそ.る, おそ.ろしい, こわ.い, こわ.がる
fear, dread, awe
JLPT3 G7 S10 F878
The relevant seal inscription form of 巩 is 工 (connecting pipe/tube) + an element combining 卩 kneeling figure with arms extended (seen also in 埶) and 手 hand/action indicator → kneel and pierce a hole in connecting two objects with a pipe/tube → secure/fasten. 恐 is 巩# + 心 heart/emotions → empty/uneasy feeling in one's heart (compare 匈), as though a hole has been pierced in it → *fear* → *threaten*; *fearsome*; *awe*; *dread* → *apprehension*; *concern* → *terrible*; *horrible*; *fierce*; *tremendous* (← aspects of a threatening or fearsome object). *Probably* and *possibly* are via the uncertainty of the state of mind that fears something desired may not in fact materialize.
[Full Kanji Etymology List]