It's the simple past tense of the verb discard.
By is not a verb and does not have participle forms; however, buy is a verb. The past participle is bought.
Like is a regular verb so the past participle is verb + ed, = liked
The past participle of the verb "be" is "been."
The past participle of the verb "study" is "studied."
Survival is not a verb and does not have participle forms. Survive is a verb, and the present participle is surviving.
It is the past participle of cleave.
The past participle of the verb die is died.
reinforced.Reinforced is the past participle of the verb reinforce.
THE PAST Participle of occur is occurred!
"Dear" is not a verb and therefore has no participle. The corresponding verb is "endear", for which the past participle is "endeared".
Dead is not a verb and does not have participle forms. The verb form is die, and the past participle is died.
Meat is not a verb and does not have participle forms. However, meet is a verb. The past participle is met.