An expert or someone who is quite knowledgeable about certain situations, especially the background of certain matters.

掴む: to grab

core, heart

circumstances / reasons

Extended shinjitai form of 摑

abduct

straight, not bent

直ぐ: immediately, right away, soon / 直ぐ: quick to / 直ぐ: right next to, right close by

(obsolete) 過ぐ: classical form of modern 過ぎる (sugiru, “to go through, to go past; to exceed”)

(obsolete) 挿ぐ: classical form of modern 挿げる (sugeru, “to connect or affix one thing to another, especially by passing something through something else”)