"Portentous" means "ominous" or foreboding. A portent is a premonition or a forewarning.

"Irrevocable" means can't be taken back, or can't be undone; final.

"Timorous" means fearful, afraid, or shuddering.

"Reckless" means careless, irresponsible or negligent.

"Frigid" means very cold, or unwelcoming.

"Apropos" means "relevant" or suitable; appropriate for a situation. The final "s" is not pronounced.

"Obedient" means compliant; describes someone who obeys.

"Grave" means very serious or gloomy.

"Inventive" means new, original, creative.

"Unsuitable" means inappropriate or not proper. It is an antonym of "apropos."

"Cardiac" means "related to the heart." For example, a heart surgery is a cardiac surgery.

"Healthy" means fit, active or strong.

"Cancerous" as an adjective means malignant, deadly or extremely harmful.

Words with the prefix "neuro" are related to the brain. For example, a brain doctor is a neurologist. 

"Pulmonary" means related to the lung. For example, a pulmonary disease is a lung disease.

"Monetary" means "financial" or related to money.

"Tedious" means boring and time-consuming.

"Sanctimonious" means self-righteous, hypocritical, smug.

"Redolent" means pleasant smelling, aromatic, or pungent.

"Plausible" means believable, possible or persuasive.

The correct answer is "complex." 

"Intricate" means very complicated or detailed.

"Complex" means consisting of many different and connected parts. The term "complex" is a synonym of the word intricate.

The adjective "enviable" means desirable, likely to be envied or wanted by others. Additionally, "cogent" means (of an argument) reasonable and convincing; "listless" means lacking energy and enthusiasm; "miserable" means very sad; "wanton" means random and destructive.

"Benign" means "mild," kindly, or not cancerous when describing a medical condition.

"Devious" means sly, sneaky, deceitful.

"Greasy" means slippery, oily, or fatty.

"Malignant" means diseased, deadly, fatal or cancerous when describing a medical condition.

"Cruel" means intentionally unkind and taking please from that unkindness; callousness towards causing others pain.

"Nefarious" means "horrible," sinful or bad.

"Ambiguous" means unclear, having more than one meaning, enigmatic.

"Defiant" means resistant, disobedient, aggressive.

"Periodic" means occurring periodically or after a certain period of time, occurring at fixed intervals.

"Amphibious" means occurring in water, aquatic. For example, amphibious creatures are creatures that live in water.

The correct answer is "related."

"Akin" is an adjective that simply means related by blood or of similar character.

The correct answer is "undisguised."

"Overt" is an adjective that means done or shown openly, making undisguised the correct answer choice.