Select the antonym (word most opposite in meaning) of "to actuate".

Introduction / Context:
This question asks you to choose the antonym of the verb "to actuate". Verbs that describe causing action or movement are common in both technical and everyday English. Understanding their opposites helps you express ideas about encouragement versus delay or obstruction. Here, your task is to identify the word that most directly expresses the opposite of setting something in motion or motivating someone to act.

Given Data / Assumptions:

• Target verb: "to actuate".
• Options: to retard, to spur, to impel, to propel and to motivate.
• We assume standard dictionary meanings.
• Actuate is often used in engineering contexts ("to actuate a valve") and in psychological or motivational contexts ("to actuate someone to action").

Concept / Approach:
"To actuate" means to put into action, to move, or to motivate. When you actuate a machine, you cause it to work. When you actuate a person, you motivate or drive them to act. The antonym, therefore, should describe delaying, slowing, or preventing action, not causing it. Among the options, "to retard" means to slow down, delay or hold back progress, which is conceptually opposite to actuating. On the other hand, "to spur", "to impel", "to propel" and "to motivate" all refer to encouraging or driving forward, which are synonyms or near synonyms of "to actuate".

Step-by-Step Solution:
Step 1: Understand "to actuate" as "to set in motion" or "to cause to act".Step 2: Examine option A, "to retard". This means to delay, slow down or hinder progress. This directly contrasts with the idea of setting in motion.Step 3: Examine option B, "to spur". To spur someone is to encourage them or urge them on, clearly similar to actuate.Step 4: Examine option C, "to impel". This means to drive or urge someone to do something, again a synonym for actuate in many contexts.Step 5: Examine option D, "to propel". This verb means to push or drive forward, especially physically, and is again in the same semantic field as actuate.Step 6: Examine option E, "to motivate". To motivate someone is to provide a reason or incentive for action, which overlaps strongly with actuate. Therefore, the only opposite is "to retard".

Verification / Alternative check:
Test the words in example sentences. "The engineer actuated the mechanism" means the engineer made it move or work. The opposite would be "The engineer retarded the mechanism", meaning slowed down or delayed it. In human terms, "The speech actuated the crowd to protest" has the opposite idea of "The speech retarded the crowd's willingness to protest", meaning it held them back. By contrast, "to spur", "to impel", "to propel" and "to motivate" would all be used in similar sentences where they could replace "actuate" without changing the general sense, confirming that they are synonyms, not antonyms.

Why Other Options Are Wrong:

• To spur: Means to urge on or encourage, similar to actuate.
• To impel: Means to drive forward or urge strongly, again close in meaning.
• To propel: Means to push or drive forward, often physically; this is about causing movement, not preventing it.
• To motivate: Means to provide reasons for acting; this is almost synonymous with actuate in psychological contexts.

Common Pitfalls:
Students sometimes grab at any familiar positive word and forget to check whether the question is about synonyms or antonyms. It is crucial to read the instruction clearly: "Select the antonym." Another pitfall is ignoring small differences in meaning and choosing a word that just "feels" strong or active. When dealing with cause-of-action verbs, always pause and ask: does this word mean to cause movement or to slow or stop it? Doing so will guide you to the correct antonym, as in this case with "retard".

Final Answer:
The antonym of "to actuate" is to retard.