A word similar in meaning to IMMINENT is:

• Imminent means about to happen in an unpleasant manner. It is an adjective.
•  For example, The company’s downfall was imminent.
• Eminent means very distinguished or very prominent.
• It's an adjective. We observe that it doesn't have a meaning like that of the given word. 
• So it not a right answer.
• Immediate means very recent or to be prompt.
• It's an adjective. We observe that it doesn't have a meaning just like that of the given word. Hence, option B isn't the proper answer.
  The future means a later period. 
• It's a noun. We observe that it doesn't have a meaning almost like that of the given word. So it an incorrect answer.
• Impending means on the brink of happen in an exceedingly bad context. it's a verb. 
• We observe that it's a meaning just like that of the given word. Hence, we are able to conclude that option D is that the correct answer.

Hence, option D is the correct answer.