Select the related word from the given alternatives: Cytology : Cells :: ? : Birds

Introduction / Context:
This analogy question checks your knowledge of scientific branches of study. Cytology is the scientific study of cells. You are asked to identify which branch of science has the same type of relationship with birds. Recognizing these subject area names is frequently tested in aptitude and general science sections of competitive exams.

Given Data / Assumptions:
- Cytology is defined as the study of the structure and function of cells.
- The second relationship must be "branch of study : subject of study" for birds.
- Among the options Odontology, Mycology, Etymology, and Ornithology, only one refers specifically to birds.
- The pattern is "X is the study of Y".

Concept / Approach:
The pair Cytology : Cells shows that the first word names a scientific discipline, while the second word names the object or subject that this discipline studies. Therefore we look for the name of the discipline that studies birds. Each option given represents a different branch of knowledge. The correct answer is the one that fits the same relationship as in the first pair.

Step-by-Step Solution:
Step 1: Interpret the relationship in the first pair. Cytology is the branch of biology that focuses on the study of cells. Step 2: Formulate the pattern as: "Name of scientific field : what it studies". Step 3: Analyze the options. Odontology is the study of teeth. Mycology is the study of fungi. Etymology is the study of the origin and history of words. Step 4: Ornithology is the branch of zoology that deals with the study of birds, including their classification, behavior, and habitats. Step 5: Therefore, Ornithology : Birds fits exactly the same relationship as Cytology : Cells.

Verification / Alternative check:
Check whether any option besides Ornithology could be reasonably connected to birds. Odontology relates only to teeth, which have no exclusive link to birds. Mycology is focused on fungi, not animals. Etymology deals with words and language. Only Ornithology consistently appears in biology and zoology as the study of birds. This confirms that the analogy is satisfied only by Ornithology.

Why Other Options Are Wrong:
Option A "Odontology" is concerned with the study of teeth, dental structure, and diseases, and does not specifically relate to birds.
Option B "Mycology" deals with fungi, such as mushrooms and molds, and therefore does not match the required subject.
Option C "Etymology" is associated with the origin of words and linguistic development, which is completely unrelated to any group of animals, including birds.

Common Pitfalls:
A common pitfall is confusing similar sounding words like Etymology and Entomology or Ornithology. Another mistake is guessing purely from partial familiarity. Instead, you should attempt to recall the exact meaning of each term. Knowing common scientific suffixes like "ology" for study, and associating them with the correct roots, helps in solving these analogy questions quickly.

Final Answer:
The correct completion of the analogy is Ornithology : Birds, so the answer is "Ornithology".