In this book, you will learn the meanings of 675 useful 15- to 18-letter words. You will also find the names of parts of speech they belong to. I have also given synonyms for most of these words. "Letter Count" has been mentioned in the bracket after each and every word. Sample this:

01 – absentmindedness [16] [n.] -- a lack of attention or awareness to what you are doing or what is happening around you [synonym: inattentiveness]
02 -- accountableness [15] [n.] -- the quality or state of being answerable or accountable
03 -- acquaintanceship [16] [n.] -- the state of being familiar to sb in a way that involves less intimate relation than friendship
04 -- acquisitiveness [15] [n.] -- excessive interest in acquiring and owning money or new possessions (material things) in a greedy way [synonyms: covetousness, hoarding, materialism]
05 -- acrimoniousness [15] [n.] -- (of an argument, a speech, discussion, behavior, etc.) the fact or quality of having strong bitter, sharp or harsh feelings and words | (b). state of having a strong unpleasant taste or smell
06 -- advantageousness [16] [n.] -- the quality or state of being good, useful, helpful or favorable in a particular situation [synonym: profitableness]
07 -- adventurousness [15] [n.] -- (a). the trait of being willing to take risks and try new ideas, methods, things or experiences | (b). a state of having full of new, exciting or dangerous ideas, methods, things or experiences [synonyms: audaciousness, boldness, daringness]
08 -- ambidextrousness [16] [n.] -- the fact or property of being equally skillful with each hand
09 – antagonistically 16 [adv.] -- In a manner that shows or feels dislike or opposition [synonym: hostility]
10 – anthropocentric [15] [adj.] -- believing that humans are the most significant or central entity of the universes
11 – anthropocentricism [18] [n.] -- the belief that humans are the most significant or central entity of the universes
12 – anthropomorphic [15] [adj.] -- treating gods, animals or objects as if they have characteristics (in terms of appearance, behavior, etc.) of human beings
13 – anthropomorphism [16] [n.] -- treatment of gods, animals or objects as if they have characteristics (in terms of appearance, behavior, etc.) of human beings
14 – approachability [15] [n.] -- the quality or state of being easy to get to [synonym: accessibility]
15 -- approachableness [16] [n.] -- the quality of being friendly and easy to meet, talk to, or deal with | (of a place) the quality of being able to be reached from a particular direction or position, or by a particular method. [synonym: accessible]
16 – argumentatively [16] [adv.] -- in a manner that shows someone wants to argue
17 – argumentativeness [17] [n.] -- the state or fact of showing tendency to argue
18 -- ascertainableness [17] [n.] -- the quality of being able to be found out, determined, fixed, etc.
19 – asymptomatically [16] [adv.] -- (of a person or illness) in a manner that shows no symptoms
20 – atmospherically [15] [adv.] -- (a). in a manner that relates to the mixture of gases that surrounds a place, earth, planet, star, etc. | (b). in a manner that creates an emotional or thrilling mood