One Word Substitution

Pivotal means crucial or critically important - it's the perfect synonym for 'very important' in a context.

A cog is a tooth on a wheel, but metaphorically refers to someone or something that serves no useful purpose. The phrase 'a cog in the machine' often implies insignificance. Among the options, only 'cog' can mean a useless or insignificant part.

To exploit means to make full use of and derive benefit from a resource. 'To make use for one's benefit' is the definition of exploitation. Spoil means to ruin, dwindle means to diminish, and swallow means to consume - none match the given meaning.

Omnivorous describes organisms that consume both plant and animal-based foods. The question explicitly asks for 'one who eats both vegetarian and non-vegetarian food,' which is the exact definition of omnivorous. Carnivorous eats only meat, hebivorous appears to be a misspelling of herbivorous (plant-eater), and eggitarian is a variant but not the standard term.

A pedagogue is a person who is involved in teaching or education. The term comes from Greek 'paidagōgos' meaning a slave who accompanied children to school. It is the correct one-word substitute for a school teacher.

Sophism originated from Greece.It implies any person practicing clever, specious reasoning.

While 'Historian' is a plausible answer, it is a broad term. Someone specifically studying the development of mankind would more precisely be an 'Anthropologist'. However, among the given options, Historian is the closest match as the other options (Oblique, Thing, Botany) are clearly incorrect.

Altur means others and ism means thinking. Thus, altruist is a person who thinks or cares for others. 

Erudite means characterized by great knowledge and learning. It is the perfect one-word substitute for a person believed to be characterized by great knowledge. The word comes from Latin 'eruditus' meaning educated or learned.

Convivialist refers to a person who is jovial and fond of festivities and social gatherings. The term comes from 'convivial' which means friendly and enjoying social gatherings. It is the correct one-word substitute for the given phrase.

Pesticide is the correct term for a chemical substance used to kill insects, especially those that damage crops or spread disease. The other options are unrelated - delete means to remove, feet are body parts, and fool refers to a foolish person.

Anesthesia is the medical term for a substance that blocks sensation, making patients unconscious or insensitive to pain during surgery. The distractors are unrelated - bloody describes appearance, zoo is an animal park, and old refers to age.

An empiric is a person who emphasizes observation and practical experience over theoretical principles in acquiring knowledge. The prefix 'empiric-' relates to empirical (based on observation/experience) rather than theoretical approaches.

Meticulous perfectly describes someone who pays extreme attention to small details and is very careful and precise in their work. The other options are completely irrelevant - theist believes in God, feet are body parts, and fool means a foolish person.

Synonym is the linguistic term for two different words that share the same or similar meanings, like 'happy' and 'joyful.' The other options don't fit - silent means quiet, duplicate means exact copy, and old refers to age.